I think (hope) we solved the coolant leak mystery on our E53

[E53inLA]

About a year ago, we replaced upper and lower radiator hoses. In the lower hose there's a temp switch with a small green O ring to make the seal. Autohaus part #13621433077.

Past few months we'd get a low coolant level message every few weeks, and I'd top it off, but never any drips in the driveway. This past weekend it finally started dripping. A couple wraps of teflon tape around that green O ring seems to solve the problem. I will order replacement part with the next order.